Thermostat



May 12, 1942. H. D. MATTHEWS THERMOSTAT Filed April 11, 1940 1 WW mo. h1 D m M o. H

wa /5 W M Pinned May UNITED STATES PATENT OFFICE THERMOSTAT Howard D.Matthews, Minneapolis, Minn., assignor to Minneapolis-HoneywellRegulator Company, Minneapolis, Minn., a corporation of Delaware IApplication April 11, 1940, Serial No. 329,125

' 2 Claims. (c1. 297-16) The present invention relates to motion comofminor convolutions A, B, etc. to Y and Z. The

pensating means for a condition responsive demlnor helix is then woundInto a majorv helix. vice, and more particularly to the structure ofAsshown in the drawing, the minor helix is rightsuch a device. handwound the the major helix is left-hand Condition responsive devices, andmore partic- 5 wound. It will also be noted that the two arcuularlybimetallic temperature responsive eleate ends II and I2 are alsoleft-hand wound.

ments, which are subjected to mediums which A motion takeoiT arm 13 isprovided onthe end contain impurities, quite frequently become sticky I2, and a suitable mounting arm I4 is formed due to deposits of theseimpurities which impede from the other compensating end H.

, the operation thereof. Particularly when the el- In windingthe'compound coiled member there ements are confined upon sliding guidesdoes this are three factors to be considered: The first facconditionprevail. With present condition retor concerns the side of the minorconvolutionssponsive elements of the compound coiled type, which is thehigh expansion metal. If the high as shown in United States Patent No.2,121,259, expansion metal is on the inside of the minor and FrenchPatent No. 710,481, and utilized-to l5 convolutions, these convolutionswill expand sticky because of continued exposure to impurihelixis wound,If the minor helix is right-hand ties, but in many adaptationsappreciably reduce Wound, d the interior metal of e me al s theeificien'cy of the element, even when perfectly the high expansionmetal, the helix will rotate clean, because of sliding friction.angularly in a counter-clockwise direction when It is an object of thisinvention to obtain optiheated; and if left-hand wound, the rotationwill mum efiiciency in a compound coiled, axially be clockwise.Obviously, if the'high expansion movable condition responsive element,by commetal Were placed 1 the t d of the m nor the appended claims, torconcerns the direction in which the major I th drawing; 3O helix iswound and, in combination with the 01:11- Figure l is an elevationalview of any device, er two factors, determines the angular directionFigure 2 is an end view looking atthe left d of movement of the entireportion ll] of the'temof Figure 1, and

Figure '3 is a diagrammatic view to illustrate fu y de ed later. that wn ny one of these the method of'computing linear movement of a threefactors is reversed, the axial movement of compound helix.

Referring now more particularly to the drawthat if two factors arechanged, the axial moveing. Thecondition responsive element is shownment W not b C an d. as comprising a compound coiled helix generallyAssume r p that t interier'metal indicated by the reference characterI0. Ends 40 0f the himetal s the high exp s n e a a d "H and [2 areprovided and are adapted to comhe xt ri r m tal is the low expansionmetal, pensate the center portion In for angular movethe minor helixbeing right hand wound and the ment upon changes in the condition'towhich the J helix being. e ha Wound, as Show element responds. Theentire element is com- Upon an increase in at e e vo u nsAto posed oftwo metals having difierent coefflicients Z Will tend t p P- It s a Wenown of expansion which are suitably secured together. phenomenon i a fii l bimetallic helix h t e I made of brass and mvar 1101'1 suitablywelded toa d t X nds t e o ate axially 'I 'heregether. The brass is thehigh expansion metal 0 fore, upon an increase in temperature the firstand the mvar iron is the low expansion metal convolution A of the minorhelix will expand and However, many other metals may be used withoutthis expansion will move the second minor helix departing from thespirit of the present inven- B toward the right as viewed in Figure 1.In tion.

thismaimer each of the convolutions in the en- The compound helix I0 iscomposed of a series tire compound helical member ID will move an Iincrementtoward the poses the degree of stance corresponding right untilthe convolutions Y and Z of the minor helix are moved a substantialdistance in this direction. For practical puraxial movement may becomputed by considering the expansion of only one of the convolutions ofthe minor helix as it would be plotted from a projection of a crosssection of one convolution taken perpendicular to the longitudinal axisthereof. lt has been found that the opposite convolution of the majorhelix will be moved a distance corresponding to the distance which itwould have been moved by the minor convolution if the connectingconvolutions were considered asbeing a link. To more clearly disclosethis principle of computation a diagrammatic Figure 3 is shown in thedrawing. In this figure a convolution c may, for practical purposes, beconsidered as mounted upon a fixed support d. The free end of the: minorconvolution c carries a link e which is connected to an uppervconvolution f and separates the two convolutions a distance equal to thediameter of the major helix. In the position shown in full lines for thelink e the bimetallic members are in their cold position. When theconvolutions of the temperature responsive element heat up the link emight be assumed to move through an angle a: for a given temperaturechange and will assume the dotted line position e. Therefore it is seenthat the upper convolution f is moved through an angle which a singlebimetal would impart to the convolution f it the convolution 0 wereconsidered as a simple bimetal loop and the connection e were a solidlink. The upper convolution f for the same temperature change willexpand an amount substantially equal to the amount of expansion of theconvolution 0, hence a lower convolution connected to the convolution Iwould be moved in a straight line substantially perpendicular to thelink e. It will be seen that the expansion of a complete convolution of'the major helix of the temperature responsive element may be computedby plotting the movement which would be imparted by a single minorconvolution in moving an upper convolution a disto a distance that theupper convolution would be moved it the two convolutions were rigidlyconnected by means of a link.

When the temperature responsive element l0 is subjected to a risingtemperature the convolution A will axially elongate, hence moving theconvolution B a slight distance away from the convolution A. Likewiseeach of the convolutions in the minor helixfrom A to Z will separatefrom each other, and the entire minor helix will be substantiallyelongated. This elongation will result in a wrapping up movement in theconvolutions Y and Z assuming that the mounting arm M is securely fixed.In addition to the angular movement caused by the minor helix there isalso a substantial angular movementinherent in the major helix.

To compensate for the angular movement of the compound helix In thearcuately shaped bimetallic pieces II and 12 are disposed at either endthereof and have the high expansion metal also on the inside of theconvolution to impart an unwrapping movement to the entire element uponan increase in temperature. It will be understood that although ends IIand i2 are both so adapted, that only one portion of the bimetal to beused to compensate the would actually need compound coil l0.

Upon cooling of verse of the above the bimetallic element theredescribed action will occur.

As has been previously'pointed out, the minor helix A to Z is right-handwound. As a result of its being right hand wound the movement of each ofthe convolutions A to Z upon being heated was toward the right inrespect to each other. It will be obvious, then, that if theconvolutions are left hand wound the movement with respect to each otherwould be toward the left and the entire element [0 will contractaxially. Whether the convolutions are either right or left hand woundthe angular or rotative movement of the element H) as a result oftemperature changes will be identical. If the high expansion metal isplaced on the outside of the minor helix the action of the element Inwill also be reversed. The rotation of the element will likewise be inthe opposite angular direction. However, if the minor helix is so wound,then the compensating ends will also have the high expansion metal onthe outside and the element In will be compensated for rotativemovement. Hence it is seen that the compensating ends H and I2 cancompensate for angular movement helix whether it is adapted to expand orcontract axially upon a given temperature change. If the major helix isright hand wound instead of left hand wound, as shown, the angularmovement of the compound coil ID will be reversed. However, thecompensating ends will also be reversed in the direction of wind and,hence, will compensate for angular movement of the temperatureresponsive element.

For the purpose of enabling others to practice my invention theaccompanying chart is presented to show various forms which mytemperature responsive element may take:

Thermostatic bimetal double helixes Movement with M h 1 M h ltincreaseto' mor our 2 01' out empera ure slde winding winding It willbe noted that when different elements of the bimetal are reversed thatthe axial movement of the element is reversed and that also the windingor unwinding of the major helix is also effected. Where a very activeelement is desired either of the types shown in 1 or 2 of theaccompanying chart may be used. These" bimetals will bevery sensitive totemperature changes inasmuch as the high expansion metal is on theoutside of the minor helix and hence more exposed to the current ofheated air or other medium to which the entire element is subjected. Itwill be noted that the type 1 opens when heated and type 2 closes whenheated. If slow responsive elements are desired either of the types5 or6 might be used where the high expansion metal is located on the insideor the minor helix, therefore making the helix respond more slowly totemperature changes. Other types may be selected as desirable for theuses to which they-are to be put. In all of the types charted there isan angular rotation of the double helix, the direction of which is'shownso that proper compensation may be provided.

of the compound While I have shown and described one form which myinvention may take 'it will be apparent that many changes will occur to-those skilled in the art. Therefore it is to be clearly understood thatI am to be limited only by the scope of the appended claims.

I claim as my invention:

1. A device of the HOWARD D. MATTHEWS.

